1. Field of the Invention
This invention relates to oil-extended hydrogenated diblock copolymers. More specifically it relates to oil-extended hydrogenated copolymers of a diblock of polybutadiene and a random copolymer of a vinyl arene and butadiene.
2. Related Prior Art
Hydrogenation of polybutadiene and of random copolymers of styrene and butadiene, as well as blends of the two hydrogenated products, do not give the thermoplastic, high temperature properties and oil acceptance desired for certain purposes. Attempts to improve these properties have resulted in the sacrifice of other desirable properties. For example, with a thermoplastic hydrogenated random copolymer of styrene and butadiene used for molding shoe soles, attempts to improve the high temperature properties by increasing the molecular weight have resulted in poor mold flow. In turn, lowering the molecular weight to improve mold flow has resulted in poor hot tensile strength. Moreover the addition of oil to improve mold flow is not practical because of the poor oil acceptability of the resin.
U.S. Pat. No. 3,598,886 discloses hydrogenated block copolymers comprising the hydrogenated product from a block copolymer consisting of a plurality of alternate blocks of polybutadiene and polystyrene.
U.S. Pat. No. 2,864,800 shows hydrogenated polybutadiene. U.S. Pat. No. 3,634,540 teaches hydrogenated block copolymers of the structure (A-B).sub.1-5 -- (B-A).sub.1-5 wherein A represents a polybutadiene block and B represents a random copolymer block of a vinyl arene and a diene in which 35-55% of its condensed units have a side chain such as methyl or ethyl. As will be noted there are two terminal hydrogenated polybutadiene blocks in the product.
British Pat. No. 1,151,598 describes a hydrogenation process used on various hydrocarbon polymers among which are included polybutadiene and copolymers of butadiene and styrene, both random and block copolymers. However, there is no teaching of a combination of blocks of polybutadiene and of random copolymer of styrene and butadiene.
Moreover, none of the products described in these prior art references show the high temperature tensile strength desired in molding compositions without sacrifice of other desirable properties.